#include <iostream>
#include <cmath>
using namespace std;
long double circle_area(long double r)
{
    return M_PI * (r * r);
}

int main()
{
    long double r;
    cin >> r;
    cout << circle_area(r) << endl;
    return 0;
}
/*
long double circle_area(long double r)
{
    return M_PI * (r * r);
}
*/
